This invention relates to a magnetically driven pump and drive mechanism and an arrangement which allows for cooling of the rotary driven member.
The Environmental Protection Agency regulations have restricted the leakage of certain liquids from gear pumps. Commonly, contact with the environment occurs either by leakage into the pump or escape of liquid from the pump. Therefore, it is common to use gear pumps with sealed magnetically coupled drives. Such magnetically coupled drives eliminate drive shaft seals, which are a major source of pump leakage and contamination of the environment.
Generally, these types of pumps have a magnetic drive mechanism with a sealed housing separating the driving and driven members. A gap is provided between the driven member and the sealed container to allow for the passage of cooling fluid to the rear portion of the rotary driven member.
Such magnetic drive mechanisms are sensitive to temperatures seen along the magnetic drive and driven surfaces. The magnetic surfaces lose strength and efficiency as temperature increases. This problem is compounded because the magnetic surfaces also lose strength as the distance between the inner and outer magnetic surfaces increases. Thus, it is common to keep the distance between the inner and outer magnetic surfaces to a minimum. However, keeping this distance to a minimum reduces the size of the gap between the fluid containment canister and the rotary driven member. Such a reduction in the width of the gap severely restricts circulation of the cooling fluid to the back side of the inner magnetic surface, thus resulting in increased temperature of the magnetic surface and decreased drive efficiency.